1. Entelodont

The Entelodont is a gentle introduction to our list. Nothing too big here, yet still savage enough to rip a man to pieces in a matter of seconds.

Standing 2.5 meters tall and weighing 400 kg on average, the Entelodont installed itself towards the top of the trophic chain. The pig-like creature lived between 35 – 16 million years ago, taking direct benefit from the relatively recent demise of all dinosaurs.

Take a better look at the above rendition of an Entelodont and imagine an encounter with one. Although having a bulky body, the evidence suggest that the Entelodont was a successful sprinter. What those teeth would do to you would be too gruesome to tell here.

2. Quetzalcoatlus

Quetzalcoatlus bones indicate a wingspan that could go as far as 20 meters, which makes the creature the biggest that ever succeeded in flying. This pterosaur most likely had a fragile frame. The small body weight was necessary just to be able to stay airborne.

Forget about asking how a Quetzalcoatlus would look next to a human! And no, you can’t ride them like dragons! We should be grateful to evolution for separating us with hundreds of million years from such beasts.

Some theories suggest that Quetzalcoatlus fed like big birds of our time, relying mostly on scavenging. Blitzkrieg raids into dinosaur nesting grounds would offer them a feast of eggs and young reptiles.

3. Gigantopithecus

Big is not always better, and a look at one of our distant kin sheds a bit of light on why we humans emerged successful as a species.

The Gigantopithecus holds the title for the biggest ape. With male adults going up to 3 meters in height and weighing over 500 kg, this was one bugger with a huge stomach to fill.

Scientists oscillate between climate change and contact with anatomically modern humans as the cause of its demise. You could compare the Gigantopithecus with a big American car trying to make its way to the European market. Fuel (food) is expensive, and the streets (habitat) are packed with others outsmarting you.

Remains found across southeast Asia indicate that Gigantopithecus lived here for millions of years before becoming extinct 100,000 years ago. A growing community argues with that claim.

For them, Gigantopithecus did not perish and is alive today in the form of Bigfoot, Sasquatch, and Yeti. Myths of shy ape-like creatures exist all over the world and evidence is piling up.

You should be glad to live in a world free of Gigantopithecus. Let’s just say that we share an important part of our DNA and that the terrifying apes could force mate with anyone foolish enough to step in their territory.

4. Deinosuchus

The name Deinosuchus translated from Greek means “terrible crocodile.”

Indeed, Deinosuchus fossils indicate that today’s crocodiles shrank over the many millions of years that separate them from their terrifying ancestors. The Cretaceous monster measured 15 meters in adulthood, a size which allowed it to play with the big guys.

It’s probably hard to picture and believe, and that’s why we included the above illustration. A mature Deinosuchus was perfectly capable of killing and eating large dinosaurs.

Ambushing terrestrial reptiles that ventured near water bodies is the only plausible explanation for the impressive proportions achieved by the Deinosuchus.

Being contemporary with the biggest crocodile that ever walked the Earth would have been a real bummer. Although highly unlikely to make a Deinosuchus belly feel full, killing that pesky agile primate would have acted like a trophy to them.

5. Andrewsarchus

Meeting an Andrewsarchus in the open would have been the nightmare of any prehistoric traveler. Fortunately for us, humankind emerged 30 million years too late to experience such a thrill.

Discovered in 1924 by an expedition that went all the way to Mongolia, the Andrewsarchus is known only from one 83 cm long skull. Yep, as frustrating as it might sound, paleontologists were unable to find any other bones.

Thus, the size and body shape of this large carnivore was left to the imagination. Take a look at the two museum exhibits. It’s obvious that modern day creatures like tigers and hyenas inspired the artists.

That long snout ceases to be an amusement once it starts digging through your carcass.

6. Titanosaurus

The Titanosaurus was a dinosaur whose discovery in the Patagonian wilderness redefined the term “big.”

40 meters long and weighing 80 tons, the Titanosaurus fully deserves its name. Being alive at the time when these majestic beasts roamed the Earth would have offered spectacular views.

Although big enough to crush an entire village in a matter of minutes, the Titanosaurus were herbivores. Scientists that put together the pieces came out with a bizarre conclusion. The giant dinosaurs were rather clumsy and died in awkward circumstances.

Forget about fending off an army of T. rex. Most Titanosaurus perished by getting stuck in the mud and starving to death. Others were huddled together by violent storms.

Take a look at the two depictions of the Titanosaurus and spot the differences. No one can say for sure how they looked like based on bone remains alone.

7. Helicoprion

The Helicoprion was a shark-like creature with one of the weirdest dentures ever assembled by Mother Nature.

The “tooth whorls” appear designed not for catching prey more efficiently, but rather for torturing the unfortunate souls. Humans were lucky enough to escape the excruciating pain induced by the teeth that worked very much like a circular saw.

The species first appeared in the fossil record 290 million years ago and managed to survive “only” 40 million years. However, that’s not the end of it.

A weird fish species related with the Helicoprion exist today. The Chimaera inhabits the deep waters and counts as a “living fossil.”

As with other animals that are long extinct, scientists face the challenge of figuring out how they looked. Only teeth survived from the Helicoprion, mostly because his body did not possess a bone skeleton.

8. Smilodon

If you think your cat hates you and plots to take over the world, you are not far from the truth.

Your feline friend longs for a period in the history of the planet when bigger cousins sat at the top of the trophic chain. The Smilodon (better known as the saber-tooth cat) is by a far margin the most notorious prehistoric mammal.

Equipped with dagger-like upper canines, this killer relied on precision killing rather than brute force. A strike at neck level was often enough to render the victims unconscious.

Don’t take the photos as facts. The coat renditions are just guess work of scientists that put on the artistic hat. It’s impossible to tell based on bone fossils alone.

You will be glad to know the 450 kg Smilodon went extinct 10,000 years ago. However, the terrifying creature can be considered as part of recent history and probably counted as the biggest enemy of humans in some geographic areas.

9. Pelagornis Sandersi

Pelagornis Sandersi is the fancy Latin name for the largest extinct flying bird.

With a wingspan exceeding 8 meters, the victims would see a huge shadow getting bigger and bigger before becoming airborne. Fortunately for us, nature doesn’t like the extremes. Evolution came to an abrupt halt for Pelagornis Sandersi which vanished some 25 million years ago. Thank God!

Call it a coincidence, but the first and only fossil of Pelagornis Sandersi was discovered at the Charleston International Airport in South Carolina. It wasn’t the stork who delivered mail and babies back then.

Don’t get too excited about the two photos depicting the large bird. Having only bones fragments to work with pushes the scientists’ imagination to its extremes.

If you hate pesky seagulls that steal your picnic basket, just imagine a creature ten times bigger wreaking havoc on the beach.

10. Titanoboa

With the dinosaurs out of the picture, a warmer than usual climate, and plenty of food, a snake species grew to unbelievable proportions.

The Titanoboa is a monster snake that will reside in your nightmares once you get to know its story. The today’s Boa looks like a worm when you put it next to the real king of the serpents.

When paleontologist uncovered remains that fitted a 12-meter long puzzle, their view of the prehistoric world changed dramatically. A one-ton snake would quickly rise to become the apex predator in his ecosystem, eating crocodiles and strangling to death much bigger creatures.

We humans came into the picture just in time to avoid such megafauna. Unfortunately for thrill seekers, our zoos are 50 million years late to be able to host such incredible reptiles.

Why did the Titanoboa not survive until today? Maybe bigger is not always better, and the species became a couch potato. Crawling 1km a day keeps extinction away.

11. Megalania

Megalania is the name of the giant lizards that might have scared to death the first human settlers that came to Australia.

Somehow similar to the today Komodo dragon, it played in its own league regarding size. Most scientists agreed that the Megalania averaged 7 meters in length, enough to freeze the blood of even the most courageous hunter-gatherer.

Cryptozoology embraced the giant goanna and placed it in the folklore of the outback. Occasional sightings of giant lizards teamed up with weird cases of cattle mutilation.

Australia is the land of “nopes, ” and no one would be surprised to add this terrifying creature on the list of threats. Its vast territory is far from being completely explored.

12. Carbonemys

We should be grateful not to be contemporary with Carbonemys, a species of giant turtle that would rival in size some of our smaller cars. The animal lived its heyday 5 million years after the dinosaur world collapsed.

The biggest tortoise to walk on the planet measured 3 meters in length. The robust mandible of its 25cm long cranium would have no problem crushing bones and ripping through flesh and muscles.

Yes, turtles are slow but don’t bet on that while trying to figure out if humans would stand a chance in a one on one confrontation. Just remember the story of the rabbit and the turtle.

13. Phorusrhacid

Let’s lose the Latin name and focus instead on what people know as Terror Birds.

Once the dinosaurs became extinct many millions of years ago, large carnivorous flightless birds took the job of bullying the animal kingdom. We know this is hard on you, picturing birds at the pinnacle of the food chain, and eating mammals as a snack.

However, fossil remains of birds from the Phorusrhacid family point out that they were as big as a Tyrannosaurus Rex. Isolated on the South American continent (which was for a long time an island), the Terror Birds became extinct 2 million years ago.

Or at least that is where the fossil record stops. More recent discoveries tend to tell a terrifying story. Smaller versions of the Terror Birds survived until 10.000 years ago.

If that is true, it means it is highly likely they made contact with the first humans that colonized the continent. Can you imagine the drama of being eviscerated by an ostrich four times taller than you?

14. Megatherium

Sloths are funny, but not when they have 4 tons and measure 6 meters from head to tail.

Megatherium is the official name given to the giant sloth, a species that thrived up until 10,500 years before present. As you probably guessed, they were hunted down by Ice Age people, like all other members of the Pleistocene’s megafauna.

The most striking feature of a Megatherium is the way it walks. One of the few bipedal mammals, the prehistoric sloth stepped on the side of its feet. His giant claws would prevent him from putting them flat on the ground.

We do hope they invent time travel soon. Seeing the giant creature in natural South American habitat could compare to nothing we have today on Earth. Ok, maybe we can picture it as an elephant with incredible front feet dexterity.

15. Megalodon

Terrified of swimming in shark-infested waters? The Megalodon can make all present day species look like dolphins.

You will be excited to know that the debate over classifying the Megalodon as extinct is far from being over. Although modern science tells us that the most powerful predator exited the stage some 2.5 million years ago, unusual sightings sketch a different story.

A large percentage of the abyss remained unexplored, and we might have a huge surprise once we turn on the lights kilometers under the water’s surface. As long as we have ships and submarines disappearing inexplicably in calm waters, the surviving Megalodon hypothesis has that 1% chance of being real.

Take a peek at the photo below. The woman in the middle gives a scale to the monster that once roamed the oceans. One 30cm tooth would be enough to gut a man to death.

Megalodon fossils indicate a total length of 20m. Given the impressive mouth opening, you could park three cars inside without worrying too much about the bumpers.

16. Meganeura

There is a big “Nope” attached to the idea of having meter large insects flying through the air and grabbing small babies from their mothers.

The Meganeura is one of the biggest flying insects that ever existed, and that’s far from being just a speculation. Take a look at the photo below and try to guess the reaction of the one who discovered it. You don’t just stumble upon a horrific fossil and live up the rest of your life in normality.

The Meganeura lived more than 300 years ago and would be proud to know its descendants survived until present day. You will pay close attention to the next dragonfly you see and thank God the Carboniferous period is long gone.

Unusual oxygen levels and the lack of more advanced predators favored a Golden Age of insects. Imagine everything you hate and fear today and multiply it ten times.

17. Ankylosaurus

Meeting an Ankylosaurus on your way to the workplace could make you stress about other things rather than your boss.

Fortunately for us humans, this excellent example of fully armored dinosaur died along with the rest of the gang around 65 million years ago. With a height of only 1.7 meters, the Ankylosaurus was tall enough to bite at neck level without putting effort into it.

Although the 6-meter long dinosaur was labeled as herbivorous by scientists, we could give credit to those depicting him as a savage, prone to kill just for fun. The Cretaceous was a time when creatures had little ethics on the agenda.

The Ankylosaurus is notorious amongst the fans of dinosaurs for having his body covered in armor plates. But it doesn’t end there. Below the shell that would make any modern day tank jealous, nature played an interesting experiment. The bones in his skull and other parts of the body are fused together, cutting out any unnecessary joint.